In fuel management systems many calculations are made to determine the amount of fuel which should be injected in the engine to maintain a predetermined air/fuel ratio. Ideally, a direct reading of the amount of air flowing into an engine and the mass of the air is desired to use in calculations for fuel consumption, ignition, etc.
Measurement of the flow of liquids such as air has been tried by many different types of meters. An air meter with the fewest or no moving parts can best withstand the environments wherein an internal combustion engine must operate.
U.S. Pat. No. 4,381,668 issued on May 3, 1983 to Sato et al and entitled "Gas Flow Measuring Apparatus" teaches a flow meter having no moving parts having a bypass section to sample flow. The section samples flow along the wall in a low pressure area and exhausts the flow from the bypass area in the center of a venturi; both locations are low pressure locations.
U.S. Pat. No. 4,304,128 issued on Dec. 8, 1981 to Hafner et al and entitled "Apparatus for Measuring the Mass of a flowing Medium," teaches the use of a temperature dependent resistor placed in a bridge circuit and the complete electronics package mounted on the meter. Air flow is sampled in a cylinder located along the axis and not across the total flow. Since the resistor is in the mainstream of the air through the meter, any reverse flow is measured giving rise to inaccurate measurements.
U.S. Pat. No. 4,304,129 issued on Dec. 8, 1981 to Kawai et al and entitled "Gas Flow Measuring Apparatus" uses an electric heater placed between two measuring resistances and all three are located in the main flow. Reverse flow of the gas is measured giving rise to inaccurate measurements.
In each of the above patents there is no immunity to reverse or back flow, therefore, the measurements are not accurate. In none is the flow across the whole meter measured, only flow along a surface or along an axially centered circular area.